Subscription television system



March 23, 1954 c. s. EILERS SUBSCRIPTION TELEVISION SYSTEM 3Sheets-Sheet 2 Filed Aug. 9

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\m m 6 Eo: .55 1% March 23, 1954 c. G. EILERS 2,673,239 SUBSCRIPTIONTELEVISION SYSTEM Filed Aug. 9, 1951 3 Sheets-Sheet 5 FIG.3 W

ILLLLLL CtffDe'ce 62 juo v| INVENTOR. CARL G. EILERS.

HIS ATTORNEY.

Patented Mar. 23, 1954 UNITED STATES PATENT OFFICE 2,673,239SUBSCRIPTION TELEVISION SYSTEM Carl G. Eilers, Fairbury, IIL, assignorto Zenith Radio Corporation, a corporation of Illinois ApplicationAugust 9, 1951, Serial No. 241,012 1 Claim. (01. 178-51) This inventionrelates to subscription television the spaced intervals determined bythe control systems and more particularly to an improved circuit toeffect coding of the television signal. system for controlling thecoding or decoding Similar apparatus is included in each subscriberapparatus utilized in such systems. receiver to effect a compensatingchange in the Patent 2,547,598 issued April 3, 1951, in the 5 scansionof the receiver reproducing device durname of Erwin M. Roschke, entitledSubscriping spaced intervals commencing and terminattion, ImageTransmission System and Apparaing during the field-retrace intervalsfollowing tus and assigned to the present assignee, disthe initiationand termination of each key-signal closes and claims a subscriptiontelevision sysburst received over the line circuit.

tem in which a coded television signal is trans- It is an object of thisinvention to provide an mitted to subscriber receivers and a key signalimprOl/ed Control y t m for Controlling the odindicating the codingschedule of the television 8 pp a us t the transmitter 01 thedecodsignal is made available at such receivers, for irig pi alatus atthe Subscriber receivers. example by distribution over a line circuit,to A more e fi j t of the invention is to enable them to decode andutilize the coded tele- 15 Provide an improved control y m forcontrolvision signal. In the Roschke system, coding of l ne th n in m hm of a p i n the television signal is accomplished by coding t v 'l y min sponse to the join pp apparatus which effects an alteration in thetiincation of a key Signal representing the coding ing between the videocomponents and synchro-- Schedule of the system and synchro P111568nizing components during spaced operating inrepresenting a timing efi tOf the ystervals, the times of occurrence of these intervals beingindicated to subscriber receivers by the key In accordance With thepresent ihVeIliiiOh, a signal. As pointed out in that patent, it isdesirn l System i pr vid f r actua in the enable that the timingalterations of the video oomcoding mechanism f a rip i n televisionponents occur during retrace intervals to pre- System under t e j tControl key clude any possibility of distortion in the television Halrepresenting t e Codi g Schedule of a coded signal which might ariseshould these alterations program Signal and p od S n l omp nents occurduring trace intervals. Moreover, it is derehreeehfihg a t m a act t o tat sirable that the bursts of key signal supplied over m h r l y m mpr ap ir f the line circuit precede the actual timing changes 6T9SS-C0I1D1edelectron-discharge d vices constiby a selected amount so that slightdelays suiw 30 tilting a trigger circuit having two S able Ope fered bythe key signal in the line circuit will ating conditions. There is afirst control tube have no adverse elfect on the coincidentoperaincluding n anode, a h d n a i nal rid tion of the coding apparatusat the transmitter having n Output Circuit Coupled o e i er in respectto the decoding apparatus at the vari- Circuit and having n put C rcuit.A Second ous receivers In order mode changes in thg control tube IS alsoprovided including an anode, television signal may occur during retraceintera Cathode and a Signal d and having an Output vals and in orderthat the key-signal bursts may Circuit 6011101661 150 the trigger ci cut and an inprecede these changes, the Roschke system pro- D 1 Circuit pde of the input and Output vides th t th key-signal generator t th tcircuits of the first control tube. Means is proitt e t d on duringrandom perigds vided for biasing the first control tube to benonginni'ng and ending during field-retrace interconductive'in hpresence of the y S al or vals, a burst of key signal appearing on the11m the per ic si n l mp nents alone and means circuit each t the keysigna1 generator is is also provided for biasing the second controlturned on Each burst f key signal is applied tube normally to translatethe periodic comto a control circuit at the transmitter jointly ponents-The System has means for Supplying he periodic components to the inputcircuits of with field-synchronizing pulses, and the control t circuitactuates the coding apparatus during the control tubes in push-pushrelation. A inst tifier is coupled to the input circuit of the firstspaced intervals determined by each burst of key signal but initiatedand terminated during the control tube Wlth Such polanty as tend tofield-retrace intervals following the initiation. snense w a rectifiedsignal and a Second rectifier and termination of each such burst. Thecoding is coupled to the input circuit of the Second Com the second.control tube non-conductive in response to a rectified signal. Finally,the control system includes means for supplying the key signal inpush-push relation to the rectifiers to effect actuation of the triggercircuit by the first control tube in response to coincidence of the keysignal and the periodic components and to effect actuation of thetrigger circuit by the second control tube in response to the presenceof the periodic signal components alone.

The features of this invention which are believed to be new are setforth with particularity in the appended claims. The invention itself,however, together with further objects and advantages thereof may bestbe understood by reference to the following description when taken inconjunction with the accompanying drawings, in which:

Figure 1 shows a subscription television transmitter similar to thatdisclosed in the aforementioned Roschke patent and incorporating acontrol system which may be constructed in accordance with theinvention,

Figure 2 is a detailed representation of the control system of thisinvention, and,

Figure 3 comprises curves useful in understanding the operation of thecontrol system of Figure 2.

The transmitter of Figure 1 includes a pictureconverting device H! ofthe cathode-ray type which may be an iconoscope, image-orthicon or thelike. Device is connected to a video amp ifier H of on or more stageswhich, in turn, is connectedto a mixer amplifier 12. The outputterminals of mixer I2 are connected through a direct-current inserter 13to a carrier-wave generator and modu ator 14 having output terminalscoupled to an appropriate antenna circuit l5. H6.

The transmitter further includes a synchronizing-signal generator l1which s pplies lineand field-synchronizing pu ses, equalizing pulses,and associated pedestals to mixer amplifier l2. Generator I1 is alsoconnected to a field-sweep system I8 and through coding apparatus IE toa line-sweep system 20, supp ying field-synchronizing pulses to thefield-sweep system and linesynchronizing pulses through the codingapparatus to the line-sweep system. The output terminals of sweepsystems I8. 20 are connected respectively to field-deflection elements2| and linedefiection elements 22 associated with device 10.

Synchronizing-signal generator [1 also supplies field-synchronizingpulses to a frequency divider 23 which may be of the random typedisclosed and claimed in copending app ication Serial No. 32,457, filedin the name of Erwin M. Roschke, on June 11, 1948, and issued March 11,1952 as Patent 2,588,413, entitled Random Frequency Dividers andassigned to the present assignee. The output terminals of frequencydivider 23 are connected to a multivibrator 24 which may be of theEccles-Jordan type. That is, the multivibrator has two stable operatingconditions and is triggered between these conditions by succeedingpulses from the frequency divider. The multivibrator is connected to akeysignal generator 25 which, in turn, is connected to a line circuit 26and to one pair of input terminals of a control system 21, the controlsystem having a further pair of input terminals connected to generator11 to derive field-synchronizing pu ses therefrom and having outputterminals connected to coding apparatus l9.

Picture-converting device In develops a video signal, representing asubject scanned by the de vice, which signal is amplified in videoamplifier H and applied to mixer 12 wherein it is mixed withsynchronizing and pedestal components from generator l1 to produce atelevision signal at its output terminals. The television signal isproperly adjusted as to background level in stage l3, modulated on apicture carrier in unit 14 and radiated to subscriber receivers overantenna l5, 16.

As previously mentioned, coding of the television signal is accomplishedby varying during spaced intervals the timing of the video componentsthereof relative to the synchronizing components. This is effected bycoding apparatus 19 which, upon actuation by control system 21, delaysby a selected amonut the timing of the line-synchronizing componentsapplied to linesweep system 20. This alters the timing of the linescansion of device I!) relative to the line-synchronizing pulsessupplied to mixer 12 from generator l1 during these intervals, and thetelevision signal may be considered effectively coded since it is notintelligibly reproducible in stand ard commercial television receiverswhich require an invariable timing of the video components relative tothe line-synchronizing components of the received television signal.

The spaced operating intervals during which coding apparatus 19 isactuated are determined in the following fashion: Frequency divider 23produces pulses which occur in time coincidence with thefield-synchronizing pulses but at a frequency which is some randomsub-multiple of the fled-synchronizing frequency. The successive pulsesfrom the frequency divider 23 trigger multivibrator 24 between itsstable operating conditions, turning on key-signal generator 25 onlyduring intervals when it is in one of its operating conditions. Eachtime the key-signal generator is actuated, it delivers a burst of keysignal to line circuit 26 for distribution to subscriber receivers.Since the multivibrator is actuated by pulses occurring in timecoincidence with fieldsynchronizing pulses, each burst of key signal isinitiated and terminated during field-retrace intervals.

The bursts of key signal are applied to control system 21. The controlsystem which also receives field-synchronizing pulses from generator l1develops an actuating signal for coding apparatus 19, the actuatingsignal having pulse components initiated and terminated during thefiefd-retrace intervals immediately following the start and conclusionof each burst of key signal. For the duration of each such pulsecomponent of the actuating signal coding apparatus [9 delays thefine-synchronizing pulses applied to linesweep system 26 by a selectedamount to efiect coding of the television signal as previously setforth.

Coding apparatus 19, therefore, changes the mode of operation of thetransmitter during spaced time intervals in response to actuation bycontrol system 21. Bursts of key signal are delivered to line circuit 26indicating the times of actuation of coding apparatus l9, but the actualoperation of the coding apparatus takes place during the field-retraceintervals immediately following the initiation and termination of eachburst. Therefore, the bursts of key signal on line circuit 26 precedethe actual mode changes at the transmitter by a time intervalcorresponding substantially to a field-trace interval so that slightdelays of the key signal in the line circuit do not adversely affect theoperation of the system. Moreover, mode changes at the transmitter occurduring field-retrace intervals and distortl'on that could arise in thetelevision signal 89 is connected to ground. Anode 85 is further h u d hch n ur uri trace in v connected to ground through a pair ofseries-conis obviated. nected resistors I01, I04. Resistor I01 has a Thearrangement of control system 2'! in acmovable tap I05 which isconnected to one of a cordance with the instant invention is shown inpair of auxiliary output terminals I06, the other detail in Figure 2.The control system has a pair auxiliary output terminal being grounded.of input terminals 5t connected to line circuit 25 The operation of thecontrol system of Figure 2 to obta n the y s nal om g n rator O e maybest be understood by reference to the curves of these terminals isconnected to ground while of Figure 3. When a key-signal burst, such asthe other is coupled to the control electrode 5| shown in curve A ofFigure 3, is applied to input of an electron-discharge device 52 througha coutermlnals 50, it is amplified in discharge device 52 plingcapacitor 53, control electrode 5| being con- Positive polarity fieldsynchronizing pulses nected to ground through a grid-leak resistor 54shown in curve B a e ap lied to input terminals charge device 62 througha, rectifier 63 and a synchronizing pulses as represented in curve 3C,limiting resistor 64. The junction of rectifier 63' whereas thenegative-polarity signal produced by and resistor 64 is connected toground through a rectifier 1| is impressed on control electrode 13 inresistor 65 shunted by a capacitor 66. Cathode conjunction with thepositive-polarity field-syn- 61 of device 62 is connected to groundthrough a ohronizing pulses as shown in curve 3D. The res sto 68 shunt dy a capacitor 69, and the cathode 37 of device 62 has a forced positivebias cathode is further connected to the positive ter- 30 thereon byvirtue of the potentiometer arrangeminal of a ource of unidirectionalpotential ment of resistors cs, 70; and these resistors are through aresistor I0, the negative terminal of the given appropriate values sothat the bias threshunidirectional potential source being connected oldof device 62 has a level shown by the dotted and resistor 12 isconnected to ground through veloped by rectifier 63; that is during theintera resistor I5 shunted by a capacitor 16. The vals of each keysignal burst across terminals 50. cathode ll of device 14 is connectedto ground The positive pulse component of the signal from through aresistor 78 shunted by a capacitor 19, rectifier 63 as well as thefield-synchronizing and the cathode is further connected to theposipulses have insuficient amplitude in and of themtive terminal B-I-of a source of unidirectional poselves to exceed this threshold value.Therefore,

tential through a resistor 80, the negative ter- 5 pulses such as shownin curve E appear in the minal of the unidirectional potential. sourcebeing plate circuit of device 52, and correspond to those connected toground. of the field-synchronizing pulses which occur The control systemincludes a further pair of, within the duration of a key-signal burstand, input terminals BI connected to generator I1 to consequently, intime coincidence with the posiobtain field-synchronizing pulsestherefrom. 59 tive pulse 0 mponents of the signal from recti- One of theterminals BI is grounded and the other fier 63. is coupled to thecontrol electrodes GI and 13 Device 74, on the other hand, has a biasthreshthrough capacitors 82 and 83, respectively. old established byresistors 78, and potential The anode M of device. 62 is connected tothe source 13-}- such that the field-synchronizing The cathode 9c ofdevice 86 is connected to rived therefrom by rectifier H, thefield-synchroground and the control electrode 9| of this device nizingpulses do not extend to the bias threshold as is connected to the anode88 of device 89 through on shown in curve D. Therefore, pulsescorrespond- Anode of device 85 is connected to the positive termediatethe key-signal bursts as shown in terminal B+ through a resistor 94 andto the curve F. More particularly, whenever a fieldcontrol electrode 95of device 89 through a re- 65 synchronizing pulse occurs Within theinterval of sistor 96, control electrode 95 being connected to akey-signal burst and establishes a resulting sigthe negative terminal C-of a biasing potential nal exceeding the bias of device 62, it istranssource through a resistor 91. Anode 80 is furlated therethrough.Otherwise the pulse is ther connected to the positive terminal B+translated by the alternate device 14. a through a resistor 98, and toground through se- 70 Devices 86 and G3 are connected as a multiriesresistors 99, I00. Resistor 99 has a movable vibrator of theEccles-Jordan type. That is, the tap ml which is connected to one of theoutput multivibrator is triggered from a first stable operterminals I02,the other output terminal being ating condition to a second stablecondition by grounded. Output terminals I02 are connected negativepulses in the plate circuit of device 62, to coding apparatus I9.Cathode IE3 of device 75 and is returned to the first condition bynegative I pulses in the plate circuit of device 14. The multivibratordevelops a signal across resistors 99, I00 having positive pulsecomponents occurring whenever the multivibrator is in its secondoperating condition; this signal is shown in curve G. Therefore,assuming that the multivibrator is in its first operating conditionwherein device 89 is predominantly conductive, the first pulse of curveE triggers the multivibrator to its second operating conditionWhereindevice 8B is predominantly conductive, but the second pulse ofcurve E has no eifect on the multivibrator since it is already in itssecond condition. However, the next succeeding pulse of curve F returnsthe multivibrator to its first operating condition in whichdevice 89 ispredominantly conductive but succeeding pulses of curve F have no efiecton the multivibrator. I'he multivibrator, therefore, de-. velops asignal across output terminals I02 having positive pulse componentsdetermined by the key signal applied to terminals 5%.. However, eachpulse component of the output signal is initiated by thefield-synchronizing pulse following the beginning of each burst of keysignal and is terminated by the field-synchronizing pulse following theending of each key-signal burst. Therefore, a series of key-signalbursts applied across input terminals 50 produces an output signalhaving a corresponding series of positive pulse components across outputterminals 102 but with each pulse component displaced a selected amountfrom the corresponding bursts as required for the proper operation ofthe control system in the transmitter of Figure 1. At the same time, asignal is developed across auxiliary output terminals lot havingnegative pulse components occurring in time coincidence with thepositive pulse components of the signal across terminals I02. Whendesired. the signal across terminals We may be used to actuate codingapparatus I5 to vary the timing of the line-synchronizing pulses appliedto sweep system 2c in the opposite sense to the variations produced bythe signal from terminals Hi2.

As described herein, the key signal occurs in bursts because itsgenerator is keyed on or off. Obviously, instead of an on-ofi relation,the generator output may be amplitude modulated between any desiredfinite limits to convey the coding information. It will be furtherunderstood that the key signal may be angular-velocity modulated todistribute coding information.

The control system of this invention has proved to be highly stable inoperation and has been used to advantage in subscription televisionsystems of the type described herein. Of course, the control system isnot limited in use to subscription transmitters; it may also be used insubscriber receivers to control decoding apparatus therein in timecoincidence with the actuation of the coding apparatus at thetransmitter.

While a particular embodiment of the invention has been shown anddescribed, modifications may be made and it is intended in the appendedclaim to cover all such modifications as may fall within the true spiritand scope of the invention.

I claim:

A control system for actuating the encoding mechanism of a subscriptiontelevision system under the conjoint control of a key signalrepresenting the coding-schedule of a coded program signal and periodicsignal components representing a timing characteristic of said signal,said control system comprising: a pair of crosscoupledelectron-discharge devices constituting a trigger circuit having twostable operating conditions; a first control tube including an anode, acathode and a signal grid having an output circuit coupled to saidtrigger circuit and having an input circuit; a second control tubeincluding an anode, a cathode and a signal grid and having an outputcircuit coupled to said trigger circuit and an input circuit independentof said input and output circuits of said first control tube; means forbiasing said first control tube to be non-conductive in the presence ofsaid key signal or said periodic signal components alone; means forbiasing said second control tube normally to translate said periodiccomponents; means for supplying said periodic components to said inputcircuits of said control tubes in push-push relation; a first rectifiercoupled to said input circuit of said first control tube with suchpolarity as to tend to render said first control tube conductive inresponse to a rectified signal; a second rectifier coupled to said inputcircuit of said second control tube with such polarity as to tend torender said second control tube non-conductive in response to arectified signal; and means for supplying said key signal in push-pushrelation to said rectifiers to effect actuation of said trigger circuitby said first control tube in response to coincidence of said key signaland said periodic components and to effect actuation of said triggercircuit by said second control tube in response to the presence of saidperiodic signal components alone.

CARL G. EILERS.

References Cited in the file of this patent UNITED STATES PATENTS NameDate Roschke Apr. 3, 1951 Number

